Blood pressure is the force blood exerts on the walls of the arteries as the heart

pumps it through the arteries. An increase in the blood volume pumped from

the heart would increase blood pressure & cause blood vessels to dilate.

It is measured as the systole & diastole pressures

where systole blood pressure accounts for the pressure when the heart contracts and

 diastolic blood pressure accounts for the pressure when the heart relaxes.

 A normal reading should be 130/80mm Hg where 130mm Hg is systolic pressure and 80

mm Hg is diastolic pressure.

How blood pressure is measured?

Blood pressure is measured in two ways:

Systolic - the highest pressure against the arteries as the heart pumps.

The normal systolic pressure is usually between 110 and 130 mm Hg.

Diastolic - the pressure against the arteries as the heart relaxes and fills with blood.

The normal diastolic pressure is usually between 70-80mm of Hg.

How the sphygnomanometer takes blood pressure?

An inflatable pressure bag is wrapped around the upper arm. The bag is connected to

a pressure-measuring instrument  called a sphygmomanometer. The operator manually

pumps up the bag with air until the circulation of the arm's main artery get interrupted.

The pressure in the bag is then slowly released until it equals the systolic pressure in

 the artery indicated by blood once again moving through the vessel. This makes a

 recorded. Next, the blood pressure in the arm's main artery drops to equal the lowest

 pressure which is the diastolic pressure. This is the pressure at which the thumping

 sound is no longer heard. This figure is also recorded.

.The operator may take numerous readings to get the true picture.

 This is because many people tend to 'tense up' during the procedure, and nervous

tension may temporarily boost the blood pressure.